Nested Electrode Geometry for Scanning Electron Microscope Ion Drift Reduction
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Solution Overview
Problem
Existing scanning electron microscope (SEM) systems using gas ionization and multiplication for secondary electron image formation face challenges in improving image forming speed and quality due to elongated ion drift time and insufficient ion multiplication ratio, primarily because the prior art does not optimize the shape of the electric field supply electrode and the distance between electrodes effectively.
Innovation Solution
The SEM system incorporates an electric field supply electrode and an ion current detection electrode arranged to cover each other, with the ion current detection electrode having a shape that efficiently detects ions generated near the electric field supply electrode, reducing the drift distance and optimizing the potential gradient for enhanced ion multiplication and detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the drift distance of secondary electrons is increased to enhance gas multiplication, then the ion multiplication ratio is improved, but the ion drift time is elongated and response speed deteriorates
Solution Approach 1:
The patent transitions from a linear electrode arrangement to a three-dimensional nested configuration where the ion current detection electrode is positioned inside the electric field supply electrode. This spatial reorganization allows ions to be detected closer to their generation point, reducing drift distance and time while maintaining effective multiplication volume.
Solution Approach 2:
The ion current detection electrode is nested within the electric field supply electrode, creating a concentric arrangement. This nesting allows the detection electrode to be positioned in the region where ions are generated through gas multiplication, minimizing the distance ions must travel to be detected while the outer electrode maintains the electric field for multiplication.
2Measurement precision
If a dedicated ion current detection electrode separate from sample holder is used, then ion detection efficiency is improved, but device complexity increases
Solution Approach 1:
The electric field supply electrode performs dual functions: it creates the electric field necessary for gas multiplication of secondary electrons and simultaneously serves as the collecting electrode for ions generated during this process. This multi-functionality eliminates the need for a separate ion detection electrode, reducing device complexity while maintaining detection efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly improves the response speed of the detection system and ion yield, resulting in higher quality SEM images by shortening ion drift time and increasing the ion multiplication ratio, compared to prior art technologies.
Implementation Method 1
Secondary electrons are multiplied in residual gas molecules around, then ionized gas ions are detected
Implementation Method 2
The secondary electrons 18 and the electrons generated by ionization are further accelerated by the electric field generated by the electric field supply electrode 23, again collide with the gas molecules and form the electron-ion pairs. As this process is repeated, the number of electrons and the number of ions increase exponentially
Implementation Method 3
The ions drift towards the ion current detection electrode 22 that is electrically connected to the sample holder 16 or is electrically insulated from the sample holder 16. The drifting ions are detected as an ion current.
Data Source
AI summary
A scanning electron microscope includes an irradiation optical system for irradiating an electron beam to a sample; a sample holder for supporting the sample, arranged inside a sample chamber; at least one electric field supply electrode arranged around the sample holder; and an ion current detection electrode.